The present invention relates to a hybrid aircraft, and more particularly, to a transmission for a rotor system within a rotor duct of a hybrid unmanned aerial vehicle (UAV).
There is an increased emphasis on the use of UAVs for performing various activities in both civilian and military situations where the use of manned flight vehicles may not be appropriate. Such missions include surveillance, reconnaissance, target acquisition, target designation, data acquisition, communications relay, decoy, jamming, harassment, ordinance delivery, or supply.
A hybrid aircraft provides the hover and low-speed maneuverability of a helicopter with the high-speed forward flight and duration capabilities of a winged aircraft. Typically, hybrid aircraft include a helicopter control surface system which provides cyclic pitch, collective pitch and differential rotation to generate lift, pitch, roll, and yaw control when operating in a hover/low-speed environment. Additionally, the hybrid aircraft includes a conventional fixed wing aircraft control surface system such as aileron, elevator, rudder and flaps to provide control when operating in a high-speed environment. Hybrid aircraft also may include a separate translational propulsive system.
Powering the multiple propulsion systems of a hybrid aircraft requires a relatively complicated transmission which must transmit power to the rotor system and translational propulsive system. The transmission is further complicated as multiple powerplants are commonly provided to assure sufficient power requirements. Coupling multiple power plants to a transmission system requires that relatively tight manufacturing tolerances be maintained. Each powerplant must also be interconnected with all the propulsion systems such that a single powerplant can drive all the propulsion systems in the event of a powerplant failure. Providing such requirements is particularly difficult in a UAV application which is relatively small and therefore requires light weight components.
Accordingly, it is desirable to provide a transmission system for a hybrid aircraft which is lightweight and uncomplicated while transmitting power from a plurality of powerplants.
A coaxial transmission system for a hybrid aircraft according to the present invention is driven by a plurality of driveshafts and drives a translational propulsion system. Each driveshaft is mounted to a pinion gear which mesh with an upper and lower counter-rotating gear. The upper and lower counter-rotating gears drive a respective upper and lower rotor shaft which powers a counter-rotating rotor system.
An angle A is defined between the driveshaft that drives a translational propulsion system and the driveshafts which drive the transmission. An angle B is defined between the two driveshafts which drive the transmission. The angles A and B must be divisible by the angle xcex8 as an integer. The angle xcex8 is defined by the formula: xcex8=(CP/R)*(180/xcfx80).
By angularly locating the driveshafts according to the present invention, proper meshing of the pinion gears and the upper and lower counter-rotating gears is assured. Moreover, tolerances are less stringent as the support structure is effectively designed around the optimal location of the driveshafts for gear meshing rather than visa versa. As the multi-bladed counter-rotating rotors include four blades each, the number of driveshafts do not equal the number of blades to reduce harmonic disturbances.
The transmission system includes an upper and lower housing which have a hard chrome plated outer surface to provide a smooth and durable surface for operation of an upper and lower swashplate.
An electric generator is mounted parallel to at least one driveshaft and is driven thereby to generate electrical power for the vehicle.
The present invention therefore provides a transmission system for a hybrid aircraft which is lightweight and uncomplicated while transmitting power from a plurality of powerplants.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
FIG. 1A is a general perspective view of a hybrid aircraft having a transmission system according to the present invention;
FIG. 1B is a top view of the hybrid aircraft of FIG. 1A;
FIG. 2A is a top view of a transmission for a hybrid aircraft designed according to the present invention;
FIG. 2B is an expanded side view of the transmission of FIG. 2A taken along the line 2Bxe2x80x942B;
FIG. 2C is an expanded sectional view of FIG. 2B taken along the line 2Cxe2x80x942C of a transmission for a hybrid aircraft designed according to the present invention;
FIG. 3A is a schematic representation of an arc length (circular pitch) between two teeth;
FIG. 3B is a geometric representation of a circular pitch; and
FIG. 4 is a partial view along aircraft and view of the gear arrangement within the transmission system.